Multilayer high clarity shrink film comprising monovinylarene-conjugated diene copolymer

ABSTRACT

We disclose a shrink film comprising a first layer comprising a monovinylarene-conjugated diene copolymer; a second layer comprising low density polyethylene (LDPE) and linear low density polyethylene (LLDPE); and a third layer comprising a monovinylarene-conjugated diene copolymer; wherein the second layer is disposed between the first layer and the third layer. We also disclose methods of using the shrink film to prepare bundled or fully enclosed groups of objects.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field ofmonovinylarene-conjugated diene block copolymers. More particularly, itconcerns multilayer shrink films comprising such copolymers andpolyethylenes.

A variety of shrink films have been available for the packagingindustry. In bundling a group of objects, a film is wrapped around thegroup of objects and then heat is applied, typically in a heat tunnel,and the film shrinks, unitizing the contents and providing rigidity andprotection during handling. In bundling a group of objects, the filmused generally only substantially shrinks in one direction, and thus theends of bundled packages are only enclosed by the shrinking of the loosefilm edges, which produces what the industry calls a “bullseye.” Alsoknown is fully enclosing a group of objects, which involves generallythe same technique, with a difference in using a film which generallyshrinks in both directions.

Films known commercially for bundling a group of objects or fullyenclosing a group of objects include monolayer polyethylene (PE) films,which have limitations of clarity and gloss due to the nature of thepolyethylene molecule. Various types and grades of ethylene homo- andcopolymers have been used.

Among the clearest known PE films are low density polyethylene (LDPE)films. However, LDPE films do not have sufficient strength and punctureresistance for some packaging applications.

In order to overcome the lower strength of LDPE films, films containinga blend of both LDPE and linear low density polyethylene (LLDPE) havealso been used commercially. An LDPE+LLDPE film generally has increasedstrength relative to an LDPE film, but often have reduced clarity andshrink. The increased strength of an LDPE+LLDPE film has allowedreductions in the thickness of the films, which may improve clarity andreduce film costs, but reduces film stiffness.

In order to increase the stiffness and strength of thinner films,triblends of LDPE, LLDPE, and high density polyethylene (HDPE) have beenused commercially. While an LDPE+LLDPE+HDPE film does have increasedstiffness relative to an LDPE+LLDPE film, it generally has both lowerclarity and lower gloss. It is the nature of HDPE to produce a film withhigher haze and poorer gloss.

The current state of the art regarding polyethylene films involves theuse of coextruded polyethylene films. These films may comprise LDPEouter layers and blends of LLDPE+HDPE in the core. Such films arereasonably glossy and clear, and have the stiffness to process incommonly available shrink bundling machinery.

However, in the interests of reducing cost, reducing materialsconsumption, and providing improved products, a need remains formaterials with good visual properties (i.e., high gloss and low haze),good physical properties (i.e., higher strength and stiffness), goodshrink properties, or some combination thereof.

SUMMARY OF THE INVENTION

In one embodiment, the present invention relates to a shrink filmcomprising a first layer comprising a monovinylarene-conjugated dienecopolymer; a second layer comprising low density polyethylene (LDPE) andlinear low density polyethylene (LLDPE); and a third layer comprising amonovinylarene-conjugated diene copolymer; wherein the second layer isdisposed between the first layer and the third layer.

In another embodiment, the present invention relates to a method ofbundling a group of objects, comprising wrapping the group of objectswith a shrink film as described above, wherein the shrink film has ahigher shrink in a first direction than in a second direction, to yielda wrapped group of objects, and heating the wrapped group of objects toa temperature and for a duration sufficient to shrink the shrink film,to yield a bundled group of objects.

In an additional embodiment, the present invention relates to a methodof fully enclosing a group of objects, comprising wrapping the group ofobjects with a shrink film as described above, wherein the shrink filmhas substantially similar shrink in both a first direction and a seconddirection, to yield a wrapped group of objects, and heating the wrappedgroup of objects to a temperature and for a duration sufficient toshrink the shrink film, to yield a fully enclosed group of objects.

The present invention can provide shrink films having visual properties(such as gloss and haze), physical properties (such as strength andstiffness), or shrink properties comparable to or superior to knownshrink films of the same or similar thickness, such as shrink filmshaving an LDPE/LLDPE+HDPE/LDPE three-layer structure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a portion of a film according toone embodiment of a shrink film according to the present invention.

FIG. 2 shows a cross-sectional view of a portion of a film according toanother embodiment of a shrink film according to the present invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In one embodiment, the present invention relates to a shrink film,comprising:

a first layer comprising a monovinylarene-conjugated diene copolymer;

a second layer comprising low density polyethylene (LDPE) and linear lowdensity polyethylene (LLDPE); and

a third layer comprising a monovinylarene-conjugated diene copolymer;

wherein the second layer is disposed between the first layer and thethird layer.

Unless specified to the contrary or apparent from the plain meaning of aphrase, the word “or” has the inclusive meaning. The adjectives “first,”“second,” and so forth are not to be construed as limiting the modifiedsubjects to a particular order in time, space, or both, unless specifiedto the contrary or apparent from the plain meaning of a phrase. A“copolymer” is used herein to refer to any polymer comprising at leasttwo types of units, e.g., two types of units, three types of units, etc.

The basic starting materials and polymerization conditions for preparingmonovinylarene-conjugated diene copolymers are disclosed in, e.g., U.S.Pat. Nos. 4,091,053; 4,584,346; 4,704,434; 4,704,435; 5,227,419;6,265,484; and 6,265,485.

“Monovinylarene,” as used herein, refers to an organic compoundcontaining a single carbon-carbon double bond, at least one aromaticmoiety, and a total of 8 to 18 carbon atoms, such as 8 to 12 carbonatoms. Exemplary monovinylarenes include, but are not limited to,styrene, alpha-methylstyrene, 2-methylstyrene, 3-methylstyrene,4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene,4-n-propylstyrene, 4-t-butylstyrene, 2,4-dimethylstyrene,4-cyclohexylstyrene, 4-decylstyrene, 2-ethyl-4-benzylstyrene,4-(4-phenyl-n-butyl)styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, andmixtures thereof. In one embodiment, the monovinylarene is styrene. Aunit of polymer, wherein the unit is derived from polymerization of amonovinylarene monomer, is a “monovinylarene unit.”

“Conjugated diene,” as used herein, refers to an organic compoundcontaining conjugated carbon-carbon double bonds and a total of 4 to 12carbon atoms, such as 4 to 8 carbon atoms. Exemplary conjugated dienesinclude, but are not limited to, 1,3-butadiene, 2-methyl-1,3-butadiene,2-ethyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene,3-butyl-1,3-octadiene, and mixtures thereof. In one embodiment, theconjugated diene can be 1,3-butadiene or isoprene. A unit of polymer,wherein the unit is derived from polymerization of a conjugate dienemonomer, is a “conjugated diene unit.”

A “monovinylarene-conjugated diene copolymer” is a polymer comprisingmonovinylarene units and conjugated diene units. The polymer can be ablock copolymer, that is, can comprise one or more blocks, wherein eachblock comprises monovinylarene units or conjugated diene units. Anyparticular block can comprise either or both monovinylarene units orconjugated diene units. If it comprises both, it can be a random block,a tapered block, a stepwise block, or any other type of block.

A block is “random” when the mole fractions of conjugated diene unitsand monovinylarene units in a section of the block are substantially thesame as the mole fractions of conjugated diene units and monovinylareneunits in the entire block. This does not preclude the possibility ofsections of the block having regularity (i.e., appearing non-random),but such regular sections will typically be present at no more thanabout the level expected by chance.

A block is “tapered” when both (a) the mole fraction of conjugated dieneunits in a first section of the block is higher than the mole fractionof conjugated diene units in a second section of the block, wherein thesecond section of the block is closer to a given end of the block and(b) condition (a) is true for substantially all sections of the block.(Depending on the size of the sections being considered, condition (a)may not be true for all sections, but if so, will be not true at no morethan about the level expected by chance).

A block is “stepwise” when a first section of the block containssubstantially all monovinylarene units of the block and a second sectionof the block contains substantially all conjugated diene units of theblock.

In one embodiment, the monovinylarene-conjugated diene copolymer is ablock copolymer comprising styrene blocks and butadiene blocks (a“styrene-butadiene block copolymer”). Exemplary styrene-butadienecopolymers are commercially available under the name K-Resin® (ChevronPhillips Chemical Co., The Woodlands, Tex.).

The monovinylarene-conjugated diene copolymer can have any proportion ofmonovinylarene units and conjugated diene units. In one embodiment, themonovinylarene-conjugated diene copolymer has from about 50 wt %:50 wt %monovinylarene units:conjugated diene units to about 90 wt %: 10 wt %monovinylarene units:conjugated diene units.

The monovinylarene-conjugated diene copolymer can further comprise otherunits known in the art for inclusion in monovinylarene-conjugated dienecopolymers.

Generally, each block is formed by polymerizing the monomer or mixtureof monomers from which the desired units of the block are derived. Thepolymerization process will generally be amenable to a relative lack ofchange in process parameters between different blocks, but the skilledartisan, having the benefit of the present disclosure, may make someminor changes in process parameters between different blocks as a matterof routine experimentation. The following descriptions of thepolymerization process will generally apply to the formation of alltypes of blocks in the inventive polymer, although certain descriptionsmay be of more or less value to forming one or more of the types ofblocks in the inventive polymer.

The polymerization process can be carried out in a hydrocarbon diluentat any suitable temperature in the range of from about −100° C. to about150° C., such as from about 0° C. to about 150° C., and at a pressuresufficient to maintain the reaction mixture substantially in the liquidphase. In one embodiment, the hydrocarbon diluent can be a linear orcyclic paraffin, or mixtures thereof. Exemplary linear or cyclicparaffms include, but are not limited to, pentane, hexane, octane,cyclopentane, cyclohexane, and mixtures thereof, among others. In oneembodiment, the paraffin is cyclohexane.

The polymerization process can be carried out in the substantial absenceof oxygen and water, such as under an inert gas atmosphere.

The polymerization process can be performed in the presence of aninitiator. In one embodiment, the initiator can be any organomonoalkalimetal compound known for use as an initiator. In a further embodiment,the initiator can have the formula RM, wherein R is an alkyl,cycloalkyl, or aryl radical containing 4 to 8 carbon atoms, such as ann-butyl radical, and M is an alkali metal, such as lithium. In aparticular embodiment, the initiator is n-butyl lithium.

The amount of initiator employed depends upon the desired polymer orblock molecular weight, as is known in the art and is readilydeterminable, making due allowance for traces of poisons in the feedstreams.

The polymerization process can further involve the inclusion of arandomizer. In one embodiment, the randomizer can be a polar organiccompound, such as an ether, a thioether, or a tertiary amine. In anotherembodiment, the randomizer can be a potassium salt or a sodium salt ofan alcohol. The randomizer can be included in the hydrocarbon diluent toimprove the effectiveness of the initiator, to randomize at least partof the monovinylarene monomer in a mixed monomer charge, or both. Theinclusion of a randomizer can be of value when forming a random ortapered monovinylarene-conjugated diene block of the present polymer.

Exemplary randomizers include, but are not limited to, dimethyl ether,diethyl ether, ethyl methyl ether, ethyl propyl ether, di-n-propylether, di-n-octyl ether, anisole, dioxane, 1,2-dimetboxyethane, dibenzylether, diphenyl ether, 1,2-dimethoxybenzene, tetramethylene oxide(tetrahydrofuran or THF), potassium tert-amylate (KTA), dimethylsulfide, diethyl sulfide, di-n-propyl sulfide, di-n-butyl sulfide,methyl ethyl sulfide, dimethylethylamine, tri-n-ethylamine,tri-n-propylamine, tri-n-butylamine, trimethylanine, triethylamine,tetramethylethylenediamine, tetraethylethylenediamine,N,N-di-methylaniline, N-methyl-N-ethylaniline, N-methylmorpholine, andmixtures thereof, among others.

When forming a particular block, each monomer charge or monomer mixturecharge can be polymerized under solution polymerization conditions suchthat the polymerization of each monomer charge or monomer mixturecharge, to form the particular block, is substantially complete beforecharging a subsequent charge. “Charging,” as used herein, refers to theintroduction of a compound to a reaction zone, such as the interior of areactor vessel.

Though not to be bound by theory, if an initiator is included in acharge, a block will typically form either de novo or by addition to theend of an unterminated, previously-formed, block. Further not to bebound by theory, if an initiator is not included in a charge, a blockwill typically only form by addition to the end of an unterminated,previously-formed, block.

A coupling agent can be added after polymerization is complete. Suitablecoupling agents include, but are not limited to, di- or multivinylarenecompounds; di- or multiepoxides; di- or multiisocyanates; di- ormultiimines; di- or multialdehydes; di- or multiketones; alkoxytincompounds; di- or multihalides, such as silicon halides and halosilanes;mono-, di-, or multianhydrides; di- or multiesters, such as the estersof monoalcohols with polycarboxylic acids; diesters which are esters ofmonohydric alcohols with dicarboxylic acids; diesters which are estersof monobasic acids with polyalcohols such as glycerol; and mixtures oftwo or more such compounds, among others.

Useful multifunctional coupling agents include, but are not limited to,epoxidized vegetable oils such as epoxidized soybean oil, epoxidizedlinseed oil, and mixtures thereof, among others. In one embodiment, thecoupling agent is epoxidized soybean oil. Epoxidized vegetable oils arecommercially available under the trademark Vikoflex® from AtofinaChemicals (Philadelphia, Pa.).

If coupling is to be performed, any effective amount of the couplingagent can be employed. In one embodiment, a stoichiometric amount of thecoupling agent relative to active polymer alkali metal tends to promotemaximum coupling. However, more or less than stoichiometric amounts canbe used for varying coupling efficiency where desired for particularproducts.

Following completion of the coupling reaction, if any, thepolymerization reaction mixture can be treated with a terminating agentsuch as water, carbon dioxide, alcohol, phenols, or linear saturatedaliphatic mono-dicarboxylic acids, to remove alkali metal from the blockcopolymer or for color control.

After termination, if any, the polymer cement (polymer in polymerizationsolvent) usually contains about 10 to 40 weight percent solids, moreusually 20 to 35 weight percent solids. The polymer cement can beflashed to evaporate a portion of the solvent so as to increase thesolids content to a concentration of about 50 to about 99 weight percentsolids, followed by vacuum oven or devolatilizing extruder drying toremove the remaining solvent.

The block copolymer can be recovered and worked into a desired shape,such as by milling, extrusion, or injection molding. The block copolymercan also contain additives such as antioxidants, antiblocking agents,release agents, slip agents, fillers, extenders, dyes, or the like.

In one embodiment, the antiblocking agent is a high impact polystyrene(HIPS), by which is meant a composition comprising any graft copolymerof styrene and butadiene. By “graft copolymer” is meant polystyreneproduced by polymerizing styrene in the presence of an unsaturatedrubber wherein the rubber becomes dispersed throughout the polystyrenein the form of discrete domains. In one embodiment the unsaturatedrubber is polybutadiene.

In the present invention, the monovinylarene-conjugated diene copolymercan be monomodal, that is, a population of copolymer molecules can haveone peak in a histogram of the population's molecular weightdistribution, or it can be polymodal, that is, have two or more peaks ina histogram of the copolymer molecules' population's molecular weightdistribution.

In the present invention, the monovinylarene-conjugated diene copolymercan be coupled or uncoupled, as described above.

As stated above, the first layer and the third layer comprise amonovinylarene-conjugated diene copolymer. In a further embodiment,either or both of the first layer or the third layer can furthercomprise polystyrene (PS). As used herein, “polystyrene” refers to anyhomo- or copolymer comprising styrene units. The first layer and thethird layer can each independently comprise from 0 wt % PS to about 75wt % PS. In one embodiment, the first layer and the third layer can eachindependently comprise from 0 wt % PS to about 50 wt % PS.

In the present invention, the monovinylarene-conjugated diene blockcopolymer can have any number of tapered blocks. In one embodiment, themonovinylarene-conjugated diene block copolymer has zero tapered blocks.In another embodiment, the monovinylarene-conjugated diene blockcopolymer has at least one tapered block.

The first layer and the third layer can be identical in composition, orcan differ in composition, such as by use of differentmonovinylarene-conjugated diene copolymers, different proportions ofmonovinylarene units and conjugated diene units in the copolymers, thepresence or absence of different additives (such as PS), or otherdifferences as will be apparent to the skilled artisan having thebenefit of the present disclosure.

The shrink film also comprises a second layer comprising low densitypolyethylene (LDPE) and linear low density polyethylene (LLDPE).

The LDPE in the second layer can be any branched homopolymer containingethylene units. Typically, the LDPE has a density of from about 0.922g/cm³ to about 0.924 g/cm³ and a melt index (MI) from about 0.25 g/10min to about 2.0 g/10 min (ASTM D1238). LDPE can be made by any processknown in the art.

In one embodiment, the LDPE is a clarity-grade LDPE. By “clarity-grade”is meant an LDPE having an MI greater than about 1.0 g/10 min and a hazeless than about 5% for a 1 mil thick film consisting of the LDPE.

The LLDPE in the second layer can be any linear copolymer comprisingethylene units and α-olefin units. Typically, LLDPEs have densities offrom about 0.915 g/cm³ to about 0.924 g/cm³ and MI values from about 0.5g/10 min to about 1.5 g/10 min (ASTM D1238), although this is anobservation and not a statement limiting the present invention. In oneembodiment, the a-olefin is selected from the group consisting of1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene.

The LLDPE can be produced by any technique, such as Ziegler-Nattapolymerization or metallocene-catalyzed polymerization, both of whichare known in the art. In one embodiment, the LLDPE is produced bymetallocene-catalyzed polymerization. A metallocene-catalyzed LLDPE canbe referred to herein as “mLLDPE.” We have observed that mLLDPEtypically has a narrower distribution of polymer molecular weights andlower haze than LLDPEs prepared by other techniques, although this is anobservation, and not a statement limiting the present invention.

Any proportion of LDPE to LLDPE can be used in the second layer. In oneembodiment, the second layer comprises greater than about 50 wt % LDPE.

The second layer can also comprise other materials, such as otherpolymers, for example, high density polyethylene (HDPE; an ethylenehomopolymer having a density greater than about 0.940 g/cm³ and an MI offrom about 0.25 g.10 min to about 1.5 g/10min (ASTM D1238)), very lowdensity polyethylene (VLDPE; a copolymer of ethylene and an α-olefinhaving a density less than about 0.912 g/cm³), or other polyethylenes,as well as other additives.

In the shrink film, the first layer and the third layer together cancomprise from about 10 wt % to about 40 wt % of the shrink film. This wt% is the total over both layers. The first layer and the third layer cancomprise equal weight portions of the shrink film, or they can compriseunequal weight portions of the shrink film. The second layer cancomprise from about 30 wt % to about 80 wt % of the shrink film. As willbe apparent to the skilled artisan having the benefit of the presentdisclosure, the total wt % of the three layers cannot exceed 100 wt % ofthe shrink film. In the event the total wt % of the three layers is lessthan 100 wt %, it will be apparent that the shrink film comprises one ormore additional layers.

As stated above, the second layer is disposed between the first layerand the third layer. It can be directly disposed therebetween, or a tielayer or layers can be used to facilitate adhesion between the secondlayer and either or both of the first layer and the third layer.

A cross-sectional view of a portion of a shrink film according to oneembodiment of the present invention is shown in FIG. 1. The first layer10 and the third layer 12 sandwich the second layer 14 (i.e., the secondlayer 14 is directly disposed between the first layer 10 and the thirdlayer 12). FIG. 1 is not necessarily to scale.

A cross-sectional view of a portion of a shrink film according toanother embodiment of the present invention is shown in FIG. 1. In thisembodiment, tie layer 20 facilitates adhesion between the first layer 10and the second layer 14, and tie layer 22 facilitates adhesion betweenthe third layer 12 and the second layer 14. FIG. 2 is not necessarily toscale.

In one embodiment, the shrink film further comprises a first tie layerbetween the first layer and the second layer, a second tie layer betweenthe third layer and the second layer, or both. The tie layer or each tielayer, if more than one, can independently comprise an ethylene-vinylacetate copolymer (EVA) or an anhydride-modified EVA. An exemplaryanhydride-modified EVA is Bynel® (Dupont, Wilmington, Del.).

The shrink film can be produced by any technique known in the art ofmonolayer and coextruded film making. Such techniques include milling,coextrusion, blow molding, injection molding, or cast molding.Generally, the shrink film can be produced by blown or cast filmtechniques. For example, the shrink film can be produced usingconventional extrusion techniques such as a coextruded cast film. Incoextrusion, two or more polymers are simultaneously extruded throughone die. Two or more extruders are used simultaneously to feed the die.In this process, various polymer melts are introduced into the die underconditions of laminar flow such that there is no intermixing, butbonding occurs at the interface between the film layers.

In a cast process, molten material flows from a flat die across thewidth of the line and onto a chilled drum, which cools the moltenmaterial. It is then trimmed and wound on a final drum into rolls offilm. In one embodiment, orientation can be introduced into the film bystretching the film prior to winding on the final drum. In anotherembodiment, orientation can be introduced by stretching as the materialis pulled from the die.

In a blown film process, while the extrusion process upstream of the dieis similar to the cast process, the die and downstream are different. Inthe blown film process, the die is annular (circular) and typicallypoints upward. This produces a cylindrical tube, which can then beclosed at the top (collapsed), resulting in a flattened tube; or thetube can be inflated and stretched to introduce orientation. This tubecan have its edges removed and then be wound into separate rolls offilm.

Generally, the shrink film can have a machine direction (the directionin which the shrink film comes off the production apparatus) and atransverse direction (the direction perpendicular to the machinedirection).

During or after preparation of the shrink film, it can be oriented, thatis, stretched in at least one direction. One example of orienting ispost-resin conversion on a tentering frame, although other techniquescan be used. If stretched in one direction, the film can be stretched ineither the machine direction or the transverse direction. Typically, acast film has a higher shrink in the machine direction than in thetransverse direction, but this is solely an observation of typicalfilms, and not a limiting description of the invention.

In one embodiment, a typical shrink film according to the presentinvention can have a thickness of about 0.5 mil to about 3.0 mil, and atsuch a thickness it can have visual properties (such as gloss and haze),physical properties (such as strength and stiffness), or shrinkproperties comparable to or superior to known shrink films of the sameor similar thickness and not comprising monovinylarene-conjugated dienecopolymers.

In another embodiment, the present invention relates to a method ofbundling a group of objects, comprising:

wrapping the group of objects with a shrink film comprising a firstlayer comprising a monovinylarene-conjugated diene copolymer; a secondlayer comprising low density polyethylene (LDPE) and linear low densitypolyethylene (LLDPE); and a third layer comprising amonovinylarene-conjugated diene copolymer; wherein the second layer isdisposed between the first layer and the third layer and the shrink filmhas a higher shrink in a first direction than in a second direction, toyield a wrapped group of objects, and

heating the wrapped group of objects to a temperature and for a durationsufficient to shrink the shrink film, to yield a bundled group ofobjects.

The shrink film can be as described above. In this embodiment, theshrink film has a higher shrink in a first direction than in a seconddirection. If oriented in one direction, the first direction can be themachine direction or the transverse direction. The second directionwould then be the other of the machine direction or the transversedirection.

Any group of objects for which bundling is desired can be used in thismethod. In one embodiment, the group of objects is a group of bottles,cans, or other discrete objects, optionally contained in a tray.

In the wrapping step, the shrink film is disposed in a substantiallycylindrical manner around the group of objects. The direction ofdisposing can be chosen as a routine matter for the skilled artisanhaving the benefit of the present disclosure, depending on the objects,the structure of the shrink film, and the desired structure of thebundled group of objects.

The result of the wrapping step is a wrapped group of objects.

After wrapping, the wrapped group of objects can be heated to atemperature and for a duration sufficient to shrink the shrink film. Thetemperature and the duration are a matter of routine experimentation forthe skilled artisan having the benefit of the present disclosure.Because the shrink film of this embodiment has a higher shrink in afirst direction than a second direction, the shrink film will typicallyonly shrink in the first direction. In one embodiment, the shrink in thefirst direction is at least about 40%. Shrinking will typically proceeduntil the film has shrunk in the first direction to contact the group ofobjects.

In another embodiment, the present invention relates to a method offully enclosing a group of objects, comprising:

wrapping the group of objects with a shrink film comprising a firstlayer comprising a monovinylarene-conjugated diene copolymer; a secondlayer comprising low density polyethylene (LDPE) and linear low densitypolyethylene (LLDPE); and a third layer comprising amonovinylarene-conjugated diene copolymer; wherein the second layer isdisposed between the first layer and the third layer and the shrink filmhas substantially similar shrink in both a first direction and a seconddirection, to yield a wrapped group of objects, and

heating the wrapped group of objects to a temperature and for a durationsufficient to shrink the shrink film, to yield a fully enclosed group ofobjects.

The group of objects can be any group of objects for which fullenclosure is desired. The shrink film can be as described above.

The wrapping step can be as described above.

The heating step can be as described above. Because the shrink film ofthis embodiment has substantially similar shrink in both a firstdirection and a second direction, the shrink film will typically shrinkin both directions. (“Substantially similar shrink” in this embodimentmeans the shrink in the first direction is no more or no less than about2-fold greater or less than the shrink in the second direction). In oneembodiment, the shrink in the first direction is at least about 40% andthe shrink in the second direction is at least about 40%. Shrinking willtypically proceed until the film has shrunk in both directions tocontact the package.

The following examples are included to demonstrate specific embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples which follow representtechniques discovered by the inventor to function well in the practiceof the invention. However, those of skill in the art should, in light ofthe present disclosure, appreciate that many changes can be made in thespecific embodiments which are disclosed and still obtain a like orsimilar result without departing from the spirit and scope of theinvention.

EXAMPLE 1

Several example and comparative films were produced. The example filmscomprised an A/B/A structure, wherein the A layers comprisedstyrene-butadiene block copolymer (K-Resin®, Chevron Phillips) andpolystyrene, and the B layers comprised LDPE and an mLLDPE. The filmswere oriented after production. In the following tables, “MD” refers tomachine direction and “TD” refers to transverse direction. Example 1AThickness (mil) 2.4 Secant Modulus (psi) MD 96,000 TD 87,000 ShrinkRatio % MD  65% TD  0% Gloss % (45 degree) 102% Haze %  5% Example 1BThickness (mil) 2.43 Secant Modulus (psi) MD 72,000 TD 68,000 ShrinkRatio % MD  69% TD  5% Gloss % (45 degree) 106% Haze %  5%

Example 1B was evaluated and found to completely and satisfactorilyshrink full cases of bottled water. Example 1C Thickness (mil) 1.6Secant Modulus (psi) MD 69,000 TD 65,000 Shrink Ratio % MD  66% TD  17%Gloss % (45 degree) 101% Haze %  5%

Comparative Examples were generally C/D/C structures, wherein the Clayers comprised LDPE and the D layers contained blends of LLDPE andHDPE. The Examples generally had higher gloss and lower haze than theComparative Examples, as well as higher toughness at lower thickness.Comparative Example C1A Comparative Example C1B Thickness (mil) 2.5Thickness (mil) 2.59 Secant Modulus (psi) MD 33,000 Secant Modulus (psi)MD 46,000 TD 38,000 TD 57,000 Shrink Ratio % MD 70% Shrink Ratio % MD75% TD 10% TD  0% Gloss % (45 degree) 69% Gloss % (45 degree) 74% Haze %11% Haze % 12% Comparative Example C1C Comparative Example C1D Thickness(mil) 2.95 Thickness (mil) 2 Secant Modulus (psi) MD 41,000 SecantModulus (psi) MD 36,000 TD 47,000 TD 43,000 Shrink Ratio % MD 76% ShrinkRatio % MD 65% TD  0% TD 15% Gloss % (45 degree) 69% Gloss % (45 degree)70% Haze % 11% Haze % 10%

The data shows that the shrink films of the Examples had increasedstiffness while maintaining strength, allowing them to be produced atthinner gauges. The stiffness of the Examples (secant modulus between65,000 and 96,000) exceeds the Comparative Examples (secant modulusbetween 33,000 and 59,000). Gloss was about 69-74% in the ComparativeExamples, versus a much higher gloss from 101% to 106% for the Examples.Haze in the Comparative Examples was about 10-12%, versus the much lowergloss of about 5% in the Examples.

In summary, the shrink film of the Examples had superior visualproperties and physical properties to the LDPE/LLDPE+HDPE/LDPE shrinkfilms of the Comparative Examples known in the art.

All of the compositions, articles, and methods disclosed and claimedherein can be made and executed without undue experimentation in lightof the present disclosure. While the compositions, articles, and methodsof this invention have been described in terms of particularembodiments, it will be apparent to those of skill in the art thatvariations may be applied to the compositions, articles, and methodsdescribed herein without departing from the concept, spirit and scope ofthe invention. All such variations apparent to those skilled in the artare deemed to be within the spirit, scope and concept of the inventionas defined by the appended claims.

1. A shrink film, comprising: a first layer comprising amonovinylarene-conjugated diene copolymer; a second layer comprising lowdensity polyethylene (LDPE) and linear low density polyethylene (LLDPE);and a third layer comprising a monovinylarene-conjugated dienecopolymer; wherein the second layer is disposed between the first layerand the third layer.
 2. The shrink film of claim 1, wherein the firstlayer and the third layer together comprise from about 10 wt % to about40 wt % of the shrink film, and the second layer comprises from about 30wt % to about 80 wt % of the shrink film.
 3. The shrink film of claim 1,further comprising a first tie layer between the first layer and thesecond layer, a second tie layer between the third layer and the secondlayer, or both.
 4. The shrink film of claim 3, wherein the first tielayer comprises an ethylene-vinyl acetate copolymer (EVA) or ananhydride-modified EVA.
 5. The shrink film of claim 3, wherein thesecond tie layer comprises an ethylene-vinyl acetate copolymer (EVA) oran anhydride-modified EVA.
 6. The shrink film of claim 1, wherein themonovinylarene-conjugated diene copolymer is a styrene-butadiene blockcopolymer.
 7. The shrink film of claim 1, wherein the first layer, thethird layer, or both further comprise polystyrene (PS).
 8. The shrinkfilm of claim 1, wherein the first layer, the third layer, or bothfurther comprise an antiblock agent, a slip agent, or both.
 9. Theshrink film of claim 8, wherein the antiblock agent is a high impactpolystyrene (PS).
 10. The shrink film of claim 1, wherein the LDPE is aclarity-grade LDPE.
 11. The shrink film of claim 1, wherein the LLDPE isa metallocene-catalyzed LLDPE (mLLDPE).
 12. A method of bundling a groupof objects, comprising: wrapping the group of objects with a shrink filmcomprising a first layer comprising a monovinylarene-conjugated dienecopolymer; a second layer comprising low density polyethylene (LDPE) andlinear low density polyethylene (LLDPE); and a third layer comprising amonovinylarene-conjugated diene copolymer; wherein the second layer isdisposed between the first layer and the third layer and the shrink filmhas a higher shrink in a first direction than in a second direction, toyield a wrapped group of objects, and heating the wrapped group ofobjects to a temperature and for a duration sufficient to shrink theshrink film, to yield a bundled group of objects.
 13. The method ofclaim 12, wherein in the shrink film the first layer and the third layertogether comprise from about 10 wt % to about 40 wt % of the shrinkfilm, and the second layer comprises from about 30 wt % to about 80 wt %of the shrink film.
 14. The method of claim 12, wherein the shrink filmfurther comprises a first tie layer between the first layer and thesecond layer, a second tie layer between the third layer and the secondlayer, or both.
 15. The method of claim 12, wherein in the shrink filmthe monovinylarene-conjugated diene copolymer is a styrene-butadieneblock copolymer.
 16. A method of fully enclosing a group of objects,comprising: wrapping the group of objects with a shrink film comprisinga first layer comprising a monovinylarene-conjugated diene copolymer; asecond layer comprising low density polyethylene (LDPE) and linear lowdensity polyethylene (LLDPE); and a third layer comprising amonovinylarene-conjugated diene copolymer; wherein the second layer isdisposed between the first layer and the third layer and the shrink filmhas substantially similar shrink in both a first direction and a seconddirection, to yield a wrapped group of objects, and heating the wrappedgroup of objects to a temperature and for a duration sufficient toshrink the shrink film, to yield a fully enclosed group of objects. 17.The method of claim 16, wherein in the shrink film the first layer andthe third layer together comprise from about 10 wt % to about 40 wt % ofthe shrink film, and the second layer comprises from about 30 wt % toabout 80 wt % of the shrink film.
 18. The method of claim 16, whereinthe shrink film further comprises a first tie layer between the firstlayer and the second layer, a second tie layer between the third layerand the second layer, or both.
 19. The method of claim 16, wherein inthe shrink film the monovinylarene-conjugated diene copolymer is astyrene-butadiene block copolymer.